Not applicable.
Not applicable.
The technology herein relates to a dual-polarized dipole antenna according to the preamble of claim 1.
As shown in DE 198 23 749 A1 (see also U.S. Pat. No. 6,333,720, entitled xe2x80x9cDual-Polarized Multi-Range Antennaxe2x80x9d), a dual-polarized dipole antenna has become known which is suitable for mobile radio networks used throughout the world, particularly the GSM900 or GSM1800 network for transmission in the 900 MHz or 1,800 MHz band.
A generic dual-polarized antenna which has become known uses a polarization orientation of xc2x145xc2x0. The antenna includes a number of dipole squares in a joint antenna housing in front of a reflector. A number of such dipole squares are usually arranged in the vertical direction for transmitting in one frequency. A further different dipole square is provided for transmitting in the other frequency band. For example, the different dipoles may be arranged between two such dipole squares arranged vertically above one another.
The horizontal half-power beam width of the antenna, which is mainly used, is 65xc2x0. To make antenna as compact as possible, two single dipoles are often connected together with the same phase in order to achieve the 65xc2x0 half-power beam width for each polarization. The dipoles are oriented at +45xc2x0 and xe2x88x9245xc2x0, respectively. This results in a so called dipole square,
The two horizontal radiation patterns of the +45xc2x0 and xe2x88x9245xc2x0 polarizations should be oriented to be coincident, if possible. Any deviation is called tracking.
To achieve a narrower vertical half-power beam width and to increase the antenna gain, a number of dipole squares are often connected together in the vertical direction. If this is done in phase, the two antennas polarized by +45xc2x0 and xe2x88x9245xc2x0 do not have any electrical depression. With an antenna dimensioned and arranged like this, there is no or only minimal tracking. The cross-polarized components of the radiation pattern are also minimal.
Today, it is mainly the xc2x160xc2x0 sector which is of significance for mobile radio. In recent years, mobile networks have become ever more dense due to the great success of mobile radio. The existing frequencies must be used more economically at closer and closer distances. It the coverage is too dense, interferences are produced. A remedy can be achieved by using antennas having a greater electrical depression, for example a depression angle of up to 15xc2x0. However, this has the unpleasant side effect that as the depression angle increases, the two horizontal patterns of the dual-polarized antennas drift apart, i.e. the horizontal pattern polarized +45xc2x0 drifts in the positive direction and the horizontal pattern polarized xe2x88x9245xc2x0 drifts in the negative direction. This leads to considerable tracking with large depression angles. Furthermore, the tracking is frequency-dependent. Similarly, the cross-polarized components of the radiation pattern follow the horizontal patterns which leads to a distinct deterioration in the polarization diversity characteristics in the xc2x160xc2x0 sector.
It is, therefore, desirable to overcome the disadvantages of the prior art and create an improved dual-polarized antenna.
Using comparatively simple means in the generic dual-polarized dipole antenna, even with a comparatively great depression, it is possible to achieve horizontal patterns do not drift apart or, at least, the drifting-apart is distinctly minimized. On the other hand, the solution according to the exemplary non-limiting illustrative implementation also provides possibilities to achieve a particular tracking, if required, for example in the case of a non-depressed radiation pattern. The resultant improved compensation for the tracking in dependence on frequency is surprising.
Due to the fact that the tracking is eliminated or at least minimized in accordance with the exemplary non-limiting illustrative implementation, the cross-polarized components of the radiation pattern are also distinctly improved. As a consequence, the polarization diversity characteristics are also improved.
A further advantage is also that the overall expenditure of cables can be reduced compared with conventional antenna installations.
The surprising solution according to the exemplary non-limiting illustrative implementation is based on the fact that two opposite parallel dipoles of a dipole square which radiate or, respectively, receive with the same polarization are not fed in parallel or with balanced cables or with separate cables. Rather, the feeding takes place only with respect to one dipole, and a connecting cable is then provided from the feed point at one dipole to the feed at the opposite second, parallel dipole.
Due to the feeding arrangement according to the exemplary non-limiting illustrative implementation, orienting the radiators to +/xe2x88x9245xc2x0 causes a frequency-dependent squinting of the dipole squares and thus also a drift of the patterns in the horizontal and in the vertical direction. It is completely surprising that this leads to a wide-band improvement in the tracking and additionally reduces the cross-polarized components without impairing the electrical depression. This is all the more surprising as the interconnection of the dipoles according to the exemplary non-limiting illustrative implementation results in a most unwanted narrow-band characteristic of the antenna from the point of view of conventional wisdom and, in addition, a disadvantageous frequency-dependence of the depression angle would be expected.
In a preferred implementation of the exemplary non-limiting illustrative implementation, the electrical length of the connecting cable corresponds to one wavelength xcex or an integral multiple thereof referred to the center frequency to be transmitted.
Such antennas usually do not comprise only one dipole square but a number of dipole squares arranged, as a rule, above one another in the vertical direction of installation and aligned at a 45xc2x0 angle to the vertical. Using the present exemplary non-limiting implementation, the tracking can now be preset differently in accordance with the requirements. In a preferred implementation of the exemplary non-limiting illustrative implementation, this can be effected, for example, by feeding, from the feed cable, only at the same side of dipoles aligned with the corresponding polarization and, connecting cables leading to the opposite dipole in the same manner for all dipoles.
A change in the amount of tracking, however, can be implemented by the fact that, for example, the feeding of four dipole squares arranged one above one another takes place with reference to the dipole on the left in three dipole squares with respect to the dipoles arranged in parallel with one another. Only with respect to one dipole square does it take place only with respect to the dipole parallel thereto on the right in an exemplary non-limiting implementation.
If, for example, with reference to four dipole squares, the feeding is only effected at the dipoles on the left in the case of two dipoles and the other half of the feeding is effected only at the dipoles on the right (the feeding with respect to the in each case second parallel dipole taking place via the connecting line), a different value is obtained for the tracking.
The degree and magnitude of the compensation value for the drifting-apart of the +45xc2x0 and xe2x88x9245xc2x0 polarized horizontal pattern component can be set correspondingly finely and compensated for. A different proportion is used which in the case of two dipoles oriented in parallel with one another, initial feeding takes place and a dipole is fed via a connecting line coming from there.
In the field of the dual- or cross-polarized antenna, the series feed which can be selected differently if necessary, and can be used for compensating for the frequency-dependence of the radiation patterns and for compensating for the tracking. This is completely surprising and not obvious.
The solution according to the exemplary non-limiting illustrative implementation also provides the further advantage that only one feed cable, provided with a cross section of correspondingly large dimension, to in each case two dipoles located offset by 90xc2x0 is provided. From these two dipoles, in each case only one connecting cable, provided with a thinner cable cross section, is conducted to the opposite dipole of a dipole square. This distinctly reduces the overall cable expenditure.